Barrel shaped mercury separator with spoked agitator

ABSTRACT

Apparatus for separating mercury from mercury containing material is disclosed. Apparatus comprises a closed horizontal generally barrelshaped vessel having ports for charging the vessel and for discharging the mercury and the treated residue, and agitating means. The vessel has opposed conical sections and a central cylindrical section. The agitating means comprises a rotatable spindle coaxially extending within the vessel and provided with a plurality of spokes varying in length to conform with the shape of the vessel. Preferably the spokes are provided with knife-like tips and they may be arranged in rows, the spokes in each row being off-set from the spokes in the next row except for those in the central cylindrical section.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and an apparatus for separating andrecovering mercury from the mercurial "soot" condensed following theroasting of mercury ore. The mercurial "soot" is a mixture of fineglobules of mercury (floured mercury), ore dust, mercury salts, ashes,tar and other condensation products, possibly arsenic and antimonycompounds, and water. Soot may contain 20 - 85% mercury. Mercuryrecovered from the separator following the lime treatment there isstored to await shipment.

2. The Prior Art

Conventional methods of treating "soot" for separation of mercurycomprise hoeing, with or without the addition of lime and application ofheat, burning, pressing in pans with stirrer or rollers, or heatingunder vacuum. Some of the methods produce relatively less yields ofmercury, and industrial hygiene is a problem. Difficulties areencountered with adequate separation of the mercury in the soottreatment and with the subsequent handling of the treated soot prior toand at the roaster.

Moreover, in at least one operating mercury plant, previously it hadbeen necessary to re-pulp the treated soot with water and pump it out tostorage and then re-lime the treated soot before returning it to theroaster. The present invention avoids these difficulties in not havingto re-pulp the treated soot before returning it to the roaster thusreducing lime consumption in the order of about 20%. Moreover, operatingtime per batch is virtually cut in half.

STATEMENT OF THE INVENTION

According to the present invention, mercury containing material frommercury condensers is treated with quick-lime in the separator agitationbeing achieved both mechanically and as a result of chemical action.Here the separated mercury is discharged from the separator vesselthrough a port equipped with a mercury seal to a storage tank. Residueis discharged through another port and returned directly to the roasterfor re-treatment. Although a slight vacuum is maintained duringoperation to prevent escape of mercury vapours, the substantiallyair-tight vessel is also equipped with ports for charging material andfor ventilation.

DETAILED DESCRIPTION OF THE INVENTION

The novel separator comprises a closed horizontal generallybarrel-shaped vessel having opposed conical end sections and a centralcylindrical section and provided with ports for charging the vessel andfor discharging the mercury and the treated residue, agitating meanscomprising a rotatable spindle coaxially extending within said vesseland provided with a plurality of spokes varying in length to conformwith the shape of the vessel. These spokes provide a shearing actionwhich allows mercury in the particles of soot to coalesce into droplets.Preferably the spokes are provided with knife-like tips. The knife-liketips keep the friction or drag effect to a minimum by cutting away thescale from the vessel wall, and hardening the surface of these tipsreduces wear.In embodiments that illustrate a preferred form of theinvention:

FIG. 1 is a flow diagram of mercury separating process illustrating theposition of the novel separator.

FIG. 2 is a side elevation of the novel separator.

FIG. 3 is a plan view of the novel separator.

FIG. 4 is an end view of part of the separator illustrating thearrangement of the spokes.

FIG. 5 is a side elevation of part of the separator illustrating thearrangement of the spokes.

Referring to FIG. 1, it will be seen that the separated mercury isdischarged from the mercury separator to a storage tank. Moreover, theresidue is discharged from the mercury separator directly to a roasterfor re-treatment.

Referring to FIGS. 2 and 3, the vessel 1 is made up of a centralcylindrical section 2 abutted by two truncated cone end sections 3, andis closed at both ends by vertical walls 4. The vessel 1 is providedwith lime-addition port 5, mercurial soot addition ports 6, ventilationports 7, and port 8 for discharging treated soot by means of a screwconveyor (not shown) to return it to the roaster as illustrated inFIG. 1. The separated mercury drains to the centrally located well 9 forautomatic discharge through a mercury seal and valve arrangement 10. Aspindle 11 is rotatably mounted within the vessel 1 in bearings 12, oneend of the spindle 11 being operably connected to a drive means 13. Thespindle 11 is provided with a plurality of spokes 14. The spokes 14 varyin length, conforming with the shape of the vessel 1; their arrangementis in parallel rows perpendicular to the axis of the spindle 11, as bestseen in FIGS. 4 and 5.

Referring to FIGS. 4 and 5, all spokes 14 of each row are of the samelength and are spaced equi-angularly and except for the three centrerows A, the spoke positions of each row are off-set from those of thenext row. The spokes 14 are provided with knife-like tips 15. Spokelengths are such that all spoke tips 15 are equi-distant from the wallsof the vessel. The tips 15 provide scraping action such that a minimumamount of material is permitted to cling to the vessel wall. In oneembodiment, there are six spokes in each of the three centre rows A. Therest of the rows (sixteen) have only four spokes, each row being off-set45° from the next. In the most preferred embodiment, the three centrerows A have eight spokes with the rest (sixteen) having six spokes each.Spokes of each row are off-set 30° from those of the next row.

It will be appreciated that in carrying out the method of the presentinvention, arrangement of, and distance between the spokes areimportant; if they are too far apart, there is no upward movement of themixture in the drum, if too close, all of the mixture is carried rightaround within the drum or bridging occurs. Under optimum operatingconditions, the spokes when in the more upward positions are free ofmixture, providing a self-cleaning arrangement. Rotation of the mixerspindle at about 14 r.p.m. tends to push the mixture well up the side ofthe drum, thus helping to keep the soot loose and permitting the mercuryto settle to the bottom. The separator is filled only to the centre linewith about 250 lbs. of lime and from about 250 to about 400 lbs. ofuntreated soot for each batch operation, and the mixing-separatingoperation takes about forty-five minutes. The direction of the spindlerotation is then reversed and the treated soot pushed up the other sideof the drum to the discharge port. Discharging takes about fifteenminutes.

In the condensed material from the launders following the condensersmuch of the mercury has already separated and more tends to coalesceimmediately. All this mercury passes through the separator on its way tothe mercury storage tank. The remainder, in the soot, is a very fineuncoalesced material which requires the lime treatment to induce furtherseparation. Normally, about 50% of the untreated soot is mercury and thetreated soot returned to the roaster has about 15% mercury content.Water content of the soot is variable, but the viscous untreatedsoot-water mix averages about 50% solids, whereas after treatment thefree moisture content is 3 to 5%. The remainder of the water is bound upin hydration of the lime. Heat released by the slaking of the limeprovides a partial drying out of the treated soot which is then dryenough for return to the roaster. The temperature of the treatedmaterial is about 65°C.

Lime treatment of the soot tends to cause a hard scale to form on theinside of the drum. By flattening the spoke tips, a dull knife edge isprovided which cuts into the scale and thus also prevents jamming andexcess vibration. Scale removal is improved by having the line of thetip edge at a 45° angle to the spindle axis, and having alternate spoketip edges twisted in opposite directions to equalize side thrust effectcreated by operation of the apparatus. Hardened spoke tips may be usedfor wear resistance, and practice has been to use Stellite (trademarkfor non-ferrous alloys of cobalt, chromium and tungsten). Because thespoke tips may provide the greatest maintenance problem, to avoidreplacement of the whole spindle including all the spokes, the endportion of each spoke, say six inches, may be made removable usingmale-female threaded sections. With the novel separator, the dry treatedsoot can be effectively discharged from the vessel by reversing spindleoperation. It is then carried by conveyors directly to a drying hearthof the roaster.

WHAT I CLAIM AS MY INVENTION IS:
 1. Apparatus for separating mercuryfrom mercury containing material comprising a closed horizontalgenerally barrel-shaped vessel, having opposed conical end sections anda central cylindrical section, and provided with ports for charging thevessel, and for discharging the mercury and the treated residue,agitating means comprising a rotatable spindle coaxially extendingwithin said vessel, and provided with a plurality of spokes, said spokesbeing arranged in rows, said rows of spokes being parallel to each otherand equally spaced along the length of the spindle, each row having atleast four spokes equiangularly positioned about the circumference ofthe spindle, the spokes in each row being off-set from the spokes in thenext row except for those in the central cylindrical section which arenot off-set, said spokes being of equal length in each row, but ofdifferent lengths in different rows, such that a constant distanceexists between the free ends of each of the spokes and the inner wall ofthe vessel.
 2. An apparatus according to claim 1 wherein the threecentre rows have eight spokes, and the remaining rows each have sixspokes, wherein the spokes of each row are off-set 30° from those of thenext row.
 3. Apparatus as claimed in claim 1 wherein the spokes areprovided with knife-like tips.
 4. Apparatus as claimed in claim 3,wherein the knife-like tips are adapted to be attached to the spokewithout detaching the spoke from the spindle.
 5. Apparatus as claimed inclaim 4, wherein the knife-like tips are adapted to be detached from thespoke without detaching the spoke from the spindle.
 6. Apparatusaccording to claim 3 wherein the knife-like tips are fabricated fromwear-resistant material.
 7. Apparatus as claimed in claim 4 wherein theknife-like tips are fabricated from wear-resistant material.